Background: Multicystic dysplastic kidney (MCDK) is a renal dysplasia characterized by the presence of multiple cysts that are non-communicating, separated by dysplastic parenchyma that consumes the renal cortex resulting in a non-functional kidney. MCDK has an incidence of 1: 4300 of live births and is usually unilateral, most commonly occurring in the left kidney. Simple MCDK is defined as unilateral dysplasia with a normal contralateral kidney but with compensatory hypertrophy of the contralateral kidney, and no associated genitourinary anomalies.
Case Report: A 21 year old Hispanic American female, presented with intermittent, sharp, severe left flank pain, fever and dysuria for two days but had gradually worsened within the last 24 hours prior to presentation. Previous history of multicystic dysplastic kidney, diagnosed four years ago. No pertinent physical examination findings except left costovertebral angle tenderness (CVAT). Urinalysis findings were positive for infection and urine culture grew pan sensitive Escherichia coli. A CT scan of abdominal and pelvis without contrast revealed a normal right kidney and left kidney had multiple non-communicating dilated cystic spaces, but no hydronephrosis, left ureteropelvic junction obstruction and finding were consistent with multicystic dysplastic kidney and also noted perinephric stranding.
Conclusions: VUR is the most common renal abnormality in patients with MCDK, occurring in about 25% of contralateral kidney. Infections involving the MCDK are rare. In fact, cases of infections such as pyelonephritis or an infected renal cyst of MCDK are almost non-existent in the current literature. This patient presented with findings consistent with MCDK complicated by pyelonephritis.

Keywords: renal cysts, Pyelonephritis, Multicystic Dysplastic Kidney